A slurry bed reactor is a common gas-liquid (slurry) contact reaction equipment and has an extremely high liquid storage capacity. As for a catalytic reaction process having very great heat of reaction, the slurry bed reactor can effectively remove heat of reaction, achieve isothermal operation of the reactor, and guarantee the normal operation of the reactor. Hence, said reactor is widely used in the current chemical engineering industry. The slurry bed loop reactor, however, is a high effective, multiphase reactor developed on the basis the slurry bed bubbling reactor. Besides all the advantages of the slurry bed bubbling reactor, the slurry bed loop reactor further enables the inner fluid to circulate in a regular manner, so as to enhance the mixing, diffusion, heat transfer and mass transfer between the reactants.
In order to eliminate the diffusion effects, the catalyst in a size of scores of micrometers, or even in the form of finer particles is generally used in the slurry bed reactor, which is also accompanied by the difficult problem of the separation of the reaction product from the catalyst particles. How to effectively achieve the liquid-solid separation becomes the key technique during the use of the slurry bed reaction.
Generally, the liquid solid separation of the slurry bed reactor catalyst slurry is carried out outside the reactor. The catalyst-containing slurry must be delivered by a special pump, and the separated catalyst still needs to be sent back to the reactor in the slurry form. Such process, however, will readily lead to breakage of the catalyst particles, so as to bring problems to the continuous operation of the reactor for a long period of time.
U.S. Pat. No. 6,068,760 and WO02/097007A2 both disclose the process for the liquid solid separation in a slurry bed reactor by using the settling technique. Said process comprises drawing the reacted slurry out of the reactor, feeding the slurry through a settling pipe and into the settling tank for settlement, discharging the supernatant as the product and recycling the heavy slurry containing a large amount of catalyst particles at the subnatant layer back to the reactor.
The separation process disclosed in EP1405664A1 comprises directly introducing the reacted slurry into the settling tank with the baffle in a height higher than the liquid level in the settling tank, so that, after the slurry flows through the gaps between the baffle and the bottom of the tank, the supernatant slowly rises and outflows from the upper part of the settling tank, and the heavy slurry containing particles is fed back to the main body of the reactor from the outlet at the bottom of the settling tank.
CN1433838A discloses the method for setting up separation units in the main body of the reactor so as to enable the slurry to achieve the liquid solid separation. Moreover, said document discloses applying a strong magnetic field at the bottom of the settling unit to speed up the liquid solid separation rate. However, the complete liquid solid separation achieved by a single settling technique to obtain the liquid product having an extremely low solid content requires a settling device having a very great volume to ensure sufficient settling time, which results in that most of the area and space of the equipment are occupied by the settling device and leads to relatively low production efficiency. The smaller the size of the catalyst is, the more favorable it is to the reaction. Meanwhile, solid powder having an extremely particle size will be produced during the reaction due to catalyst abrasion. The effect of the settling technique for the catalyst particles in a size of several micrometers, or even in a smaller size, however, is not good. Since the Fischer-Tropsh Synthesis reactor has a relatively great diameter, the magnetic field device is difficult to produce homogeneous magnetic field in the reactor. Moreover, the reactor is cumbersome and expensive, and cannot degauss the magnetized catalyst to prevent the magnetized catalyst from agglomeration, which all affect the normal operation of the reactor.
WO94/16807 discloses the process for achieving the liquid solid separation using filtration pack in the reactor. However, the regeneration of the filtration pack is difficult once the filtration pack is blocked up by the catalyst particles. Thus the process is not suitable for large-scale continuous production.
CN1589957A discloses the process for achieving the liquid solid separation by disposing the primary separation unit inside the reactor and the secondary separation unit outside the reactor. In addition, the back purging unit is disposed outside the reactor to carry out the continuous operation of filtration. This not only occupies the reaction space inside the reactor, but also results in complex equipment structure and complicated operation.
US2005/0027021A1 discloses a liquid solid separation system. Said system achieves the liquid solid separation by setting up the vertical filtering units outside the reactor. The filter cake deposited on the filtering units performs a primary filtration function, and the thickness of the filter cake is adjusted by adjusting the flow velocity of the slurry. However, since the space of the units has been designed and determined, the range to be adjusted by controlling the filtering rate purely by adjusting the flow velocity of the slurry outside the units is greatly limited. Furthermore, fine particles easily block up the filtration medium, and there is no effective back purging method, which results in that the continuation of the filtration is difficult to achieve.
US2005/0000861A1 discloses a filtering unit capable of being disposed inside and/or outside the reactor. Said unit comprises a rough filtration section and a fine filtration section coaxially and vertically disposed in the same diameter. The upper rough filtration section prevents the catalyst having large particles from entering the filtration section and recycles back to the reactor. The filtrate through rough filtration will be directly fed to the fine filtration section below the rough filtration section for further filtration and separation. Such liquid solid separation process recurs to the external force. However, no detailed back purging method is provided. Thus the continuous effective liquid solid separation is difficult to fulfill.
From the analyses above, it can be seen that it requires greater area, even valuable reaction space, to purely use the settling process. The continuous operation cannot be achieved by using the filtering method. Even if the continuous operation is achieved, the separation efficiency will be lowered due to higher solid content. Moreover, the equipment will be rendered complex, and the investment and operation cost will be increased.